Large-scale production of aligned long boron nitride nanofibers by multijet/multicollector electrospinning

Boron nitride nanofibers (BNNFs) with alignment and large length have been prepared on a large scale by electrospinning the precursor fibers and subsequent nitridation. A multijet/multicollector electrospinning system is constructed by simply arranging three jets and three tip collectors abreast. By this system the aligned precursor fibers with lengths over 13 cm are collected throughout a very large length of 68 cm. The alignment of the electrospun precursor fibers is mainly induced by the converging electric field generated by the applied tip collectors. Composite B₂O₃/polyvinylbutyral (PVB) fibers (BOFs) were used as the precursor fibers, where PVB was added for increasing the spinnability of the electrospinning solutions. However, the presence of PVB in the BOFs results in the formation of carbon residue in the nitrided products, which is a stubborn problem for preparing the BNNFs. We successfully solved this problem by introducing a small amount of O₂ at appropriate temperature during nitridation with NH₃. The morphology of the nitrided products is strongly dependent on the diameter and B₂O ₃/PVB ratio of the BOFs and the BNNFs with diameters as small as below 100 nm were obtained by controlling them. The obtained BNNFs were crystallized with (002) base planes preferentially oriented in parallel to the fiber axis. A high onset oxidation temperature of 890 °C was demonstrated for the BNNFs.